Weight Loss Induces Changes in Vitamin D Status in Women with Obesity but not in Men: a Randomized Clinical Trial.

Context: Obesity is associated with low vitamin D and recent studies have suggested a difference in vitamin D metabolism between females and males.

Objective: The aim of this study was to investigate the effects of weight loss on vitamin D status in individuals with obesity, and secondarily, whether vitamin D metabolism differs between women and men.

Methods: Secondary analysis from a randomized placebo-controlled trial, designed to investigate the efficacy of 52 weeks of treatment with either liraglutide, exercise or combined, compared with placebo on weight loss maintenance after an 8-week low-calorie diet-induced weight loss in 195 individuals with obesity (BMI 32-43 kg/m2).

Results: The low-calorie diet-induced weight loss resulted in an increase in serum 25(OH)D in both women and men (12 nmol/L (95%CI 9-15) and 13 nmol/L (95%CI 8-17); p < 0.001 for both). Women who experienced a further weight loss during the 52 weeks of intervention had an increase in serum 25(OH)D compared with women regaining weight (14 nmol/L (95%CI 6-22); p = 0.001). Interestingly, women experiencing further weight loss at week 52 had a lower serum 25(OH)D at baseline compared with women regaining weight (54 nmol/L (SD 19) vs. 70 nmol/L (SD 25); p < 0.001).

Conclusion: Weight loss induced by a low-calorie diet resulted in an increase in serum 25(OH)D in both women and men. Only in women, further weight loss had an additional beneficial impact on vitamin D. Additionally, initial low serum 25(OH)D was associated with successful weight loss maintenance in women, but not men.